1. Field of the Invention
The present invention relates to the field of torsional vibration dampers, and particularly to vibration dampers adapted to be mounted on rotary shafts such as the crankshaft of an internal combustion engine.
2. Description of the Prior Art
Dampers of this type are employed to reduce tortional vibrations, and find extensive use in the automotive and diesel engine industry. Torsional vibrations are delivered intermittently to the crankshaft, and the angular vibrations may be of considerable magnitude, possibly resulting in gear damage and fatigue failure of the crankshaft.
The purpose of a torsional vibration damper is to reduce the amplitude of the vibrations. Vibration dampers convert the vibrational energy to thermal energy in the damping action. The absorption of the vibrational energy lowers the strength requirements of the shaft, and therefore lowers the required weight of the shaft. The damper also has a direct effect on inhibiting vibration of various other components of the internal combustion engine which would be affected by the crankshaft vibration.
A common form of prior art dampers includes a hub attached to the crankshaft to rotate therewith. The periphery of the hub may carry an elastomer member which in turn is coupled to an outermost, inertia member. During the engine operation, the torsional damper serves to lessen the magnitude of the angular vibrations of the crankshaft to which it is attached. Torsional vibration dampers are also known which employ a liquid of high viscosity. Such an arrangement is afforded by a hub member which carries a closed, annular cavity therein, the annular cavity being filled with a liquid of high viscosity and with an annular inertia member. The only coupling between the inertia member and the hub, the latter being connected to the crankshaft, is the viscous liquid. The prior art also includes dampers which employ both viscous and elastomer components.
Several patents show vibration dampers including both an elastomer and a viscous fluid. In U.S. Pat. No. 3,200,485, issued to McGavern on Aug. 17, 1965, there is disclosed a damper having a hub defining an annular cavity and an inertia member secured therein. An elastomer couples the hub with the radially inner and outer walls of the cavity, and a viscous fluid is received between the inertia member and the bottom wall of the cavity. In U.S. Pat. No. 3,495,459, issued to McLean on Feb. 17, 1970, there is disclosed a tuned viscous damper having an annular inertia mass received within a housing. Elastic "tuning springs" are connected to the housing by a viscous damping fluid.
A vibration damper is disclosed in U.S. Pat. No. 3,992,963, issued to Nov. 23 1976, which includes a first inertia member coupled to a hub by an elastomer, and a second inertia member within an annular cavity in the hub and surrounded by a high viscous liquid. A vibration damper including a hub with elastomeric members sandwiched between the hub and an inertia ring, and further including a viscous shear fluid in an annular, internal cavity in the hub, is described in U.S. Pat. No. 4,339,963, issued to Bremer on July 20, 1982.
A viscous torsional vibration damper is disclosed in U.S. Pat. No. 3,555,926, issued to Moorhouse et al. on Jan. 19, 1971. The damper includes an annular housing and an inertia ring received in the housing, with a viscous damping fluid therebetween. A similar viscous fluid damper is shown in U.S. Pat. No. 3,640,149, issued to McLean on Feb. 8, 1972. Elastomer dampers, having an elastomer located between and coupling a hub member and an inertia ring, are disclosed in U.S. Pat. Nos. 4,318,309, issued to Bremer on Mar. 8, 1982; 3,410,369, issued to Ishizuka on Nov. 12 1968; and, 4,341,130, issued to Shepherd et al. on July 27, 1982.